R help - Oct 2010 - Splitting a DF into rows according to a column

Hi,

I'm turning my wheels on this and keep coming around to the same wrong 
solution - please have a look and give a hand ...

The premise is: a DF like so
> loremIpsum <- "Lorem ipsum dolor sit amet, consectetur adipiscing
elit.
Quisque leo ipsum, ultricies scelerisque volutpat non, volutpat et nulla. 
Curabitur consequat ullamcorper tellus id imperdiet. Duis semper malesuada 
nulla, blandit lobortis diam fringilla at. Vestibulum nec tellus orci, eu 
sollicitudin quam. Phasellus sit amet enim diam. Phasellus mattis hendrerit 
varius. Curabitur ut tristique enim. Lorem ipsum dolor sit amet, consectetur 
adipiscing elit. Sed convallis, tortor id vehicula facilisis, nunc justo 
facilisis tellus, sed eleifend nisi lacus id purus. Maecenas tempus 
sollicitudin libero, molestie laoreet metus dapibus eu. Mauris justo ante, 
mattis et pulvinar a, varius pretium eros. Curabitur fringilla dui ac dui 
rutrum pretium. Donec sed magna adipiscing nisi accumsan congue sed ac est. 
Vivamus lorem urna, tristique quis accumsan quis, ullamcorper aliquet 
velit."
> tmpDF <- data.frame(Column1=rep(unlist(strsplit(loremIpsum," 
")),length.out=510),Column2=runif(510,min=0,max=1e8))

is to be split into DFs with 50 entries in an ordered manner according to 
column2 (first DF ist o contain the rows with the 50 largest numbers, ...).

Here is what I have been doing:
> binSize <- 50
> splitMembership <- 
pmin(ceiling(order(tmpDF[["Column2"]],decreasing=TRUE)/binSize),floor(nrow(tmpDF)/binSize))
> splitList <- split(tmpDF,splitMembership)
Distribution seems to work ...
> sapply(splitList,nrow)
But this is NOT what I wanted ...
> sapply(splitList,function(x){max(x[["Column2"]])})
This was supposed to give me bins that are Column2-sorted and bin one should 
have a higher max than 2 than 3 ...

Can anyone point out where (my now 3 reimplementations) fail?

Thanks, Stupid Joh

On Oct 4, 2010, at 16:57 , Johannes Graumann wrote:
> Hi,
> 
> I'm turning my wheels on this and keep coming around to the same wrong 
> solution - please have a look and give a hand ...
> 
> The premise is: a DF like so
> 
>> loremIpsum <- "Lorem ipsum dolor sit amet, consectetur
adipiscing elit.
> Quisque leo ipsum, ultricies scelerisque volutpat non, volutpat et nulla. 
> Curabitur consequat ullamcorper tellus id imperdiet. Duis semper malesuada 
> nulla, blandit lobortis diam fringilla at. Vestibulum nec tellus orci, eu 
> sollicitudin quam. Phasellus sit amet enim diam. Phasellus mattis hendrerit
> varius. Curabitur ut tristique enim. Lorem ipsum dolor sit amet,
consectetur
> adipiscing elit. Sed convallis, tortor id vehicula facilisis, nunc justo 
> facilisis tellus, sed eleifend nisi lacus id purus. Maecenas tempus 
> sollicitudin libero, molestie laoreet metus dapibus eu. Mauris justo ante, 
> mattis et pulvinar a, varius pretium eros. Curabitur fringilla dui ac dui 
> rutrum pretium. Donec sed magna adipiscing nisi accumsan congue sed ac est.
> Vivamus lorem urna, tristique quis accumsan quis, ullamcorper aliquet 
> velit."
>> tmpDF <- data.frame(Column1=rep(unlist(strsplit(loremIpsum," 
> ")),length.out=510),Column2=runif(510,min=0,max=1e8))
> 
> is to be split into DFs with 50 entries in an ordered manner according to 
> column2 (first DF ist o contain the rows with the 50 largest numbers, ...).
> 
> Here is what I have been doing:
> 
>> binSize <- 50
>> splitMembership <- 
>
pmin(ceiling(order(tmpDF[["Column2"]],decreasing=TRUE)/binSize),floor(nrow(tmpDF)/binSize))
>> splitList <- split(tmpDF,splitMembership)
> 
> Distribution seems to work ...
>> sapply(splitList,nrow)
> 
> But this is NOT what I wanted ...
>> sapply(splitList,function(x){max(x[["Column2"]])})
> This was supposed to give me bins that are Column2-sorted and bin one
should
> have a higher max than 2 than 3 ...
> 
> Can anyone point out where (my now 3 reimplementations) fail?
> 
> Thanks, Stupid Joh
Dear Stupid Joh, 

Have you considered something along the lines of

o <- order(-x$Column2)
xx <- x[o,]
split(xx, (seq_len(NROW(x))-1) %/% 50)

The above is a bit hard to follow, but it seems to work better with rank()
instead of order():
> splitMembership <- 
+
pmin(ceiling(rank(-tmpDF[["Column2"]])/binSize),floor(nrow(tmpDF)/binSize))
> splitList <- split(tmpDF,splitMembership)> sapply(splitList,nrow)
 1  2  3  4  5  6  7  8  9 10 
50 50 50 50 50 50 50 50 50 60 
> sapply(splitList,function(x){max(x[["Column2"]])})
       1        2        3        4        5        6 
99877498 90567877 81965382 69112280 59814266 52130373 
       7        8        9       10 
41557660 32630212 21226996 11880032 


-- 
Peter Dalgaard
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com